(1) Field of the Invention
The present invention relates to a rotary cutting die assembly that is comprised of separable component parts. In particular, the invention pertains to a rotary cutting die assembly comprised of a mandrel having a cutting cylinder and drive gear slip fit thereon. The drive gear is connected in driving engagement with the sleeve and both move relative to the mandrel during cutting operations performed by the assembly. The cutting cylinder is deformable on the mandrel while performing the cutting operations of the assembly and is replaceable when worn. The rotary cutting die assembly of the present invention enables reductions in material costs, heat treatment costs, and shipping costs from those costs associated with manufacturing and distributing conventional rotary cutting dies.
(2) Description of the Related Art
Prior art rotary cutting die presses commonly employ a rotating cutting die and a rotating anvil roll mounted parallel to the cutting die on the press. Mating gears connected with the cutting die and the anvil roll cause the die and roll to rotate in synchronism with each other. The cutting die and anvil roll rotate against each other as stock material or a web of stock is passed through the press between the rotating die and anvil. A pressure assist roll or a load carrying truck or tractor assembly is often employed to exert a downward force on the die and cause it to bear against the anvil roll. As the material passes between the rotating die and anvil, a cutting configuration formed on the exterior surface of the cutting die cuts sections of material from the web. The shape of the sections of material cut from the web correspond to the configuration of the cutting edges of the die.
Self adhesive labels or pressure sensitive labels and other similar articles are commonly provided in rolls of such labels. The rolls are made up of a plurality of self stick labels attached to a continuous length of backing material. The self stick labels are readily removed from the rolls of backing material by merely peeling the labels from the material.
Rotary production of pressure sensitive labels is accomplished by passing a web of pressure sensitive label stock comprising the label material, a layer of pressure sensitive adhesive, and a backing layer to which the adhesive holds the label, material, between a rotary cutting die and a smooth anvil roll rotatably mounted on a die cutting press. As set forth above, the cutting die has an exterior cylindrical surface with cutting edge configurations formed thereon. The configuration of the die cutting edges is determined in accordance with the shapes desired of the labels to be cut from the label stock. As the label stock is passed between the cutting die and the anvil roll of the press, labels are produced by crush cutting through the label material and the layer of pressure sensitive adhesive, to the backing layer of the stock. The cutting die does not cut through the backing layer and the above described operation forms a continuous sheet of self adhesive labels that may be removed from the backing.
Rotary cutting dies of the type used in preparing label strips are commonly formed from a solid steel cylinder. The cylinder is large enough in diameter to provide a peripheral surface area sufficient in size to accommodate several cutting edge configurations required for a desired label shape or set of label shapes to be cut from label stock. The diameter of the cylinder is also chosen to provide sufficient strength to the cylinder to prevent any deflection of the cylinder during rotary cutting operations of the press.
The cutting edge configurations are typically engraved on the exterior surface of the rotary cutting die by various methods such as mechanical milling, chemical milling or spark erosion. The dies are also formed with journal shafts protruding from their opposite ends. The journal shafts are used in mounting a gear on the rotary cutting die, and for rotatably mounting the die in a rotary die cutting press. The gear mounted on the shaft is fixed stationary relative to the cutting die and meshes with a gear of the press to impart rotation to the cutting die. The gear mounted on the die meshes with a gear on the anvil roll of the press to deliver a rotational force to the anvil roll and to maintain the rotary cutting die, the anvil roll, and other operations performed by the rotary cutting press in synchronism.
The opposite ends of the cutting die, just inside of the journal shafts, are formed with a cylindrical bearing surface having a diameter that is equal to or slightly greater than the diameter of the peripheral surfaces of the cutting edges. These opposite surfaces of the die form bearing rolls. The bearing rolls maintain constant the distance of the anvil roll axis from the cutting die axis for proper mesh of the cutting die gear and the anvil gear of the press and for controlling the distance of the die's cutting edges from the anvil roll.
A variation of the above described prior art cutting die provides an undercut magnetic area between the bearing rolls of the cutting die. The area is undercut to accept a flexible steel sheet having the desired cutting edge configurations engraved thereon.
Rotary cutting dies of the type described above are disadvantaged in that they are expensive to manufacture, and correspondingly expensive to replace when worn. Because the diameter of a rotary cutting die must be made large enough to both prevent center deflection of the die during a cutting operation and to provide adequate surface area for the plurality of cutting edge configurations desired on the die, a significant materials cost is involved in the manufacture of a rotary cutting die. Because the cost of heat treating a die is based on the weight of the die, the more material used in manufacturing the die correspondingly increases the costs involved in heat treating the die. Moreover, because shipping costs are directly related to the weight of the product being shipped, the costs involved in delivering the cutting dies to purchasers is also directly related to the weight of materials involved in manufacturing the die.
Accordingly, it would be advantageous to provide a method of making a rotary cutting die as an assembly of component parts, where one component part of the assembly comprising the cutting edge configurations is separable from the remainder of the assembly after a period of wear, and is replaceable by a new component part. Such an assembly would reduce the materials cost involved in manufacturing an entire rotary cutting die to replace a die whose cutting edges have worn. Such an assembly would also reduce the heat treatment costs, which are based on weight, involved in manufacturing a replacement rotary cutting die in that only the component part being replaced need be heat treated.
Such an assembly would also reduce the shipping costs involved in replacing a worn rotary cutting die in that only the component part replacing the worn component part need be shipped.
The present invention overcomes the problems associated with conventional rotary cutting dies by providing a rotary cutting die assembly comprised of several component parts, with each component part being separable from the assembly and replaceable, thereby reducing the costs of material, heat treatment, and shipping associated with replacing an entire worn rotary cutting die of the prior art.